My calculations say that with isp=250 you need a mass fraction of about 20 to get to orbit, neglecting gravity losses and air drag. With gravity and drag it is more like 40. That is in agreement with the other calculations above.

So given that SS1 has a mass fraction of only 3, have we decided that power should be back in the unsolved category?

By the way, I was reviewing a video of Rutan's speech at the university of Texas (looking for that orbital statement) and in it he says that the navigation system in SS1 is capable of orbital operation. That puts us back to my first guess, where power and reentry are not solved and environment and navigation are.

Just adding in some of my own thoughts on this interesting discussion. I'm sure I remember Burt talking about the first orbital vehicle being a single person vehicle (probably in an internet article). Taking this into account shouldn't WK II be large enough as the carrier vehicle? As it already needs to carry 9 people above the height of SS1 plus two pilots and 7 passengers who will watch the launch. In this way the orbital vehicle would be what SS1 it to SS2, a technology demonstrator before a larger operational vehicle is built. Does this not mean that power is unlikely to be one of Burt's problems especially when using a more powerful engine.

When applied to a SS1 oriented vehicle can the CXV re-entry technology be easily applied? If I remember correctly SS1 has a very fast re-entry (in terms of time taken) is this an advantage or disadvantage with orbital re-entry.

Just a final comment if Burt wants to create a seat of the pants orbital vehicle like SS1 then this could be one on the unsolved list. Making the vehicle safe enough to be flown hands on. Though I woud be suprised if the ping pong ball and string hasnt been modified or improved upon for SS2

Consider the facts that A) once in orbit, you have to expend energy to deorbit, thus placing yourself in control of your reentry speed (unlike in suborbital flight, when you're simply falling, and your speed is determined by your zenith; and B) the orbital variant of SS1 will undoubtedly have a better glide path than the Brick-that-is-the-Space-Shuttle, and thus make a hands-on reentry much much safer.

broyale, welcome to the boards!

Oh, and Peter, I just noticed that you have exactly 666 posts. A perfect time for your addition to the ranks of the Explorers, Sigurd's own Legion of Doom.

I'm sure I remember Burt talking about the first orbital vehicle being a single person vehicle (probably in an internet article).

I've never heard that, do you have a link?

That is probably the one I have been remembering and looking for. I have not found it online yet. As I recall it was during a press conference and seemed more like an offhand remark about how much more propellant would be required to put SS1 in orbit than any real idea to do something. He also said the pilot would have EXTREMELY limited space and nobody would want to stay in orbit that way. It sounded wrong to me at the time and after looking at the numbers in detail it seems even more wrong to me now. He probably later realized it was wrong and that is why it has never been mentioned again.

Speaking at a lecture organised by the Manx Festival of Aviation at the Royal Aeronautical Society in London, the aerospace designer detailed how such an orbital vehicle could be evolved from his existing three-man, suborbital 3,000kg (6,600lb) SpaceShipOne. The amount of spacecraft mass dedicated to fuel would be increased to achieve the greater altitude and speed required.

"We'd have a small cramped cabin for the orbital flight and you'd be in it for a long time. You'd want to go to a hotel [because of that] and for orbital tourism you'd want an altitude of 130km," says Rutan.

The Flight International article was where I have read about Burt talking about a one person orbital craft, but thinking back I may also have seen footage of his lecture at the Royal Aeronautical Society broadcast on SKY's interactive news in the UK (They did a lot of extended coverage at this time on the interactive news service that I don't think they put on the regular broadcast and can be worthwhile checking out from time to time if your in the UK).

At the time I was also pretty suprised at the low altitude of the space station mentioned. Often on space forums people talk about 200km or greater for orbital spacecraft and stations. Wouldn't a 130km orbit improve the payload fraction mass of an orbital vehicle, even if only by a small amount and as a secondary bonus reduce any threat from orbital debris?

BRoyale and CampbelP:
I do also remember something about a one-man orbital craft derived from SS1. I seem to remember he made a comment like that not long after SS1's success- I may well be wrong. The part about people not wanting to stay in orbit makes sense, relative to Rutan's businesslike character. The ship ride is cramped, so you'll want an actual destination, like an orbiting hotel. More captial that way. But if i was on a spacecraft, i would be happy regardless of the cramped accomodations.
I'm also confused as to why he would consider such a low orbit for a station. Maybe he's thinking of some lighter-than-air, inflatable station? (Sound ridiculous?)

A space station in a 130km orbit would decay rapidly and reenter the atmosphere within a few days.

Using my admittedly crude reentry simulation from the Aerobraking and reentry thread, I calculate it wouldn't even last one orbit. First I set up a circular orbit at 130 km with the drag term set to zero and confirmed it made one complete orbit at 130 km. When I added the drag term back in, it reentered before completing one orbit. By comparison a 400 km orbit is still at 400 km (rounded to the nearest whole kilometer) after completing one orbit, even with the drag term included. It stayed at 200 km too. At 170 it lost 1 km per orbit.

I read that with 130 km too, but what if he said (and was quoted wrong) or meant 130 miles (You'll never know those Americans with their miles, foot and inches preference )? I'm currently putting the whole SS2/SS3 information in a single file so that we can have an overview about what he or some other person from Scaled/Virgin Galactic ever said about their plans.

The article had been posted somewhere at this board and I referred to it in another thread - but I can't find it currently. I used the thread or post as a source of information and got - among others the answer that the author of the article and the journalists had to be suspected to have done an error.

I myself explicitly thought of the possibility that there has occurred an error regarding the unit of distance - miles may have been exchanged by kilometers and Rutan originally and really may have been talking about 135 miles altitude instead of 135 km altitude.

135 miles are 216 km.

I will continue to look for the threads.

Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

EDIT: In between I found the article I used as well as the thread I referred to it:

I simply had recognized that Rutan had been speaking of an altitude the artilce had reported Nautilus will be installed at. This caused argumentation against the reported altitude of 130 km or 135 km for Nautilus.

As a consequence I think Nautilus really will be installed at a significant higher orbit and that Rutan didn't intend really to go to an orbit of 135 km altitude. He might have intended to illustrate that he could achieve that orbit in principle - - to achieve it doesn't mean to keep it.

in the initial post of this thread you mentioned and asked for the two unsolved problems Rutan was speaking about.

In the following posts this has been discussed a bit without result.

In between Rutan has said something additional regarding breakthroughs - the article "Burt Rutan on Civilian Spaceflight, Breakthroughs, and Inside SpaceShipTwo" ( www.space.com/news/060811_rutan_interview.html ) he is quoted as follows: [quote]â€œMy bottom line is that we have to have some kind of breakthroughs,â€